Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Memoryless relay protocols have increasingly become popular thanks to their low complexity, small processing delay, and low energy consumption. Such relay protocols may be primarily categorized into three types: amplify-and forward (AF), detect-and-forward (DF), and estimate and-forward (EF). In general, any implementation that resolves symbols and digital data before re-encoding and transmitting again (including DF and some AF implementations) is a “hard” forward since the original signal is lost. Relay protocols where the signal is retransmitted based on phase and magnitude (including EF and some AF implementations) are known as “soft” forwards as they can be exploited by data reconstruction strategies at the end of the relay.
A performance of a practical wireless network including several relay nodes may be largely determined by the intermediate relay functionality. Any wrong decision that is made at the early hops can lead to severe error propagation to the later hops and may be detrimental to the network performance The idea of forwarding soft rather than hard information is an effective option to combat this kind of error propagation. Instead of transmitting hard decision symbols from the relay, a soft forwarding method such as EF may maximize the generalized signal-to-noise ratio (GSNR) at the destination and may outperform AF and DF in many configurations. However, GSNR optimality may not guarantee bit error rate (BER). Furthermore, EF systems cannot exploit the hybrid-automatic repeat request (H-ARQ) rapid retransmission systems that are built into Long Term Evolution (LTE) and similar standards. Thus, any data errors in an EF system may result in packet re-requests that impact network congestion.